\begin{tabular}{l*{9}{c}}
\toprule
                    &\multicolumn{3}{c}{Linear}            &\multicolumn{3}{c}{Quadratic}         &\multicolumn{3}{c}{Cubic}             \\\cmidrule(lr){2-4}\cmidrule(lr){5-7}\cmidrule(lr){8-10}
                    &\multicolumn{1}{c}{(Premium)}&\multicolumn{1}{c}{(High)}&\multicolumn{1}{c}{(Low)}&\multicolumn{1}{c}{(Premium)}&\multicolumn{1}{c}{(High)}&\multicolumn{1}{c}{(Low)}&\multicolumn{1}{c}{(Premium)}&\multicolumn{1}{c}{(High)}&\multicolumn{1}{c}{(Low)}\\
\midrule
Relative supply     &      -0.632&      -0.414&       0.218&      -0.703&      -1.029&      -0.327&      -0.608&      -1.117&      -0.509\\
                    &     (0.069)&     (0.127)&     (0.123)&     (0.077)&     (0.140)&     (0.139)&     (0.104)&     (0.158)&     (0.103)\\
\addlinespace
Real minimum wage   &      -0.220&      -0.104&       0.117&      -0.199&       0.083&       0.282&      -0.133&       0.022&       0.155\\
                    &     (0.048)&     (0.059)&     (0.058)&     (0.059)&     (0.077)&     (0.066)&     (0.052)&     (0.091)&     (0.063)\\
\addlinespace
Time                &       0.021&       0.020&      -0.002&            &            &            &            &            &            \\
                    &     (0.002)&     (0.003)&     (0.002)&            &            &            &            &            &            \\
\midrule
\bottomrule
\end{tabular}
